This invention pertains to an improved two-stage catalytic hydroconversion process for hydrocarbon feedstocks. It pertains particularly to such a two-stage process for petroleum feedstocks containing fine particulate solids in which the second-stage reactor uses less severe conditions and larger size catalyst than for the first stage reactor.
In the hydroconversion of heavy petroleum feedstocks using two-stages of catalytic reaction to produce lower boiling hydrocarbon liquid products, all the liquid fraction from the first stage is usually passed through the second stage reaction, which results in excesssive conversion of lower boiling liquids in order to obtain adequate high conversion of the high boiling fractions. Examples of such two-stage processes for petroleum feedstocks are disclosed in U.S. Pat. No. 3,418,234 to Chervenak at al, U.S. Pat. No. 3,870,623 to Johson, et al, U.S. Pat. No. 3,893,911 to Rovesti and U.S. Pat. No. 3,901,792 to Wolk et al. Also, it is usually desired to recycle a portion of the vacuum residuum material for further reaction and increased conversion to lower boiling products, as shown by U.S. Pat. No. 3,412,010 to Alpert et al. A two-stage process for hydroconversion of coal-derived liquids is disclosed by U.S. Pat. No. 3,844,933 to Wolk et al. However, for some feedstocks particularly those containing some fine particulate solids such as tar sands bitumen, a build-up of solids usually occurs in the second reactor. These problems are advantageously resolved in the present invention by withdrawing an intermediate liquid product following the first stage reaction and by using larger size catalyst in the second stage reactor.